[Swift] Inline arrays (#8755)

Implements InlineArrays which allow us to use Flatbuffers arrays within
Structs natively, and also implements FlatbufferVectors as a secondary API
when using mutable Structs

Fixes mutations within fixed sizes arrays

Adds tests and remove inout and mutating from generated objects in favor of borrowing

---------

Co-authored-by: Wouter van Oortmerssen <aardappel@gmail.com>

swift/Sources/FlatBuffers/FlatBufferObject.swift

@@ -69,5 +69,5 @@ public protocol ObjectAPIPacker {
   static func pack(_ builder: inout FlatBufferBuilder, obj: inout T) -> Offset
 
   /// ``unpack()`` unpacks a ``FlatBuffers`` object into a Native swift object.
-  mutating func unpack() -> T
+  func unpack() -> T
 }